The properties of our everyday spectral microclimate

The CIE illuminant D65 is widely adopted as defining the standard spectral power distribution (SPD) for ‘average’ daylight. Thus daylight indoors is generally assumed to approximate the SPD for D65. The weight of research on the non-visual effects of light now suggests that a key consideration for the long-term health and well-being of occupants should be the amount, duration, timing and, importantly, the spectral profile of illumination received at the eye. Measurements of the SPD of illumination were made at a number of locations outdoor and indoors. In an outdoor environment, the spectral properties of the visible sky dictate the resultant SPD largely irrespective of the surrounding built environment. Only those indoor locations with close proximity to windows exhibit a spectral microclimate comparable to daylight, while all others are dominated by the artificial light sources. Early findings indicate the need to carry out further research to more clearly understand the experienced spectral microclimate.